PicDude wrote:

> Not surprisingly, when running a compass sensor in my car, I'm running into
> interference (incorrect sensor outputs) from all the other electronics and
> metal in the car.

> Anyone know where these sensors are typically mounted in a vehicle?

  Short answer:  Use GPS, you need to be moving, but it's a small price to pay.

  Longer answer:
  Basically, it should be mounted anywhere where it will work within the
calibration limits of the compass.  If it doesn't have calibration adjustments
(mechanical or electronic) don't even try using it.

  My magnetic compass came with instructions to point the vehicle to north
(using other known methods) some distance from any surrounding metal, overhead
wires etc, then go though the calibration adjustment (point NSE & W) till it
reads correctly.

  I had it down to within a few degrees.

  In use, it was a different story.  Every time you remove or install a piece
of equipment in your vehicle, you have to check it doesn't interfere with the
compass, and re-calibrate if it does.

  While sitting at traffic lights, the adjacent lane (if moving) would cause
the compass to swing back and forth each time a car passed me.

  While driving in a steady straight line on the freeway (no other surrounding
cars) the compass would sometimes swing back and forth due to surrounding steel
barriers and such.


  In the end, I found it so useless (because I couldn't guarantee the "purity"
of my environment where I needed it) that I relied on GPS only.  The compass
was for backup just in case GPS went down.

  Now, if I need backup, I carry two GPS recievers.
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